Residential and commercial air conditioning and heat pump systems are known to employ modified automotive heat exchangers, which are desirable for its proven high heat transfer efficiency, durability, and relatively ease of manufacturability, as heat pump heat exchangers. A conventional automotive heat exchanger typically includes an inlet manifold, an outlet manifold, and a plurality of refrigerant tubes hydraulically connecting the manifolds for refrigerant flow therebetween. Corrugated fins interconnect adjacent refrigerant tubes to increase the available heat transfer area, as well as to increase the structural integrity of the heat exchanger. The core of the heat exchanger is defined by the refrigerant tubes and interconnecting corrugated fins.
Heat pump heat exchangers, also known as heat pump coils, are capable of operating as an evaporator and as a condenser. A heat pump system typically includes two heat pump heat exchangers, one located outdoors and the other indoors. When the heat pump system is in cooling mode, the indoor heat pump heat exchanger operates in evaporator mode and the outdoor heat pump heat exchanger operates in condenser mode. Inversely, when the heat pump system is in heating mode, the indoor heat pump heat exchanger operates in condenser mode and the outdoor heat pump coil operates in evaporator mode.
To meet the demands of residential and commercial applications, the size of the core of the heat pump heat exchanger has to be increased accordingly, which in turn dramatically increased the lengths of the inlet and outlet manifolds. For a heat pump heat exchanger operating in evaporator mode, the increased length of the manifolds tends to result in refrigerant mal-distribution through the refrigerant tubes. The effects of momentum and gravity, due to the large mass differences between the liquid and gas phases, can result in separation of the phases in the inlet manifold and cause poor refrigerant distribution through the refrigerant tubes. Poor refrigerant distribution degrades evaporator performance and can result in uneven temperature distribution over the core.
To assist in providing uniform refrigerant distribution through the refrigerant tubes, an inlet distributor having a plurality of uniformly spaced orifices is disposed within the inlet manifold for distributing the two-phase refrigerant throughout the length of the inlet manifold. Similarly, an outlet collector having a plurality of uniformly spaced orifices is disposed within the outlet manifold for collecting the vapor refrigerant throughout the length of the outlet manifold. Since refrigerant is in a vapor phase, its volume, vapor velocity, and the resulting pressure drop along the outlet manifold or outlet collector are much higher than if it remained in a liquid phase.
Outlet pressure drop in the outlet collector reduces performance by both constraining refrigerant flow, inducing refrigerant flow mal-distribution, and raising the core inlet pressure and temperature. Accordingly, there remains a need for a heat pump heat exchanger that has an improved outlet collector to provide for a reduced outlet pressure drop and more uniform refrigerant distribution throughout the core.